Process of producing a screened work copy of an original to be reproduced



Patented Feb. 7,1939- PATENT OFFICE ri'cocass or raonucme a scaannnn.womr corr or AN oamnnn To an PRODUCED Wilhelm SchIlIlP,

Berlin, Germany one-third to Paul A. Hennlg, Hohokna, N. 1.; andone-third to Sydney Kopp New Ifork,

No Drawing. Application June 11, 1937,

Serial No. 14'L675 4 Claims. (01. 95-5).

For reproducing'black-white drawings, pictures etc. I have alreadyproposed to use a positive or negative screened work copy of theoriginalwhich copy is photographically transferred to a print- 5 ingplate and whicli'has been obtained by the aid of a screened negative andtwo continuous-tone negatives; the continuous-tone negatives serve ascontrolling means and compensate the flattening of the tint values dueto the subdivision of the screened negative into dots. Inthis processfilms are preferably used assensitive carriers.

With regard to the three mentioned negatives the following conditionsare to be considered. The main or-screenednegative generally 18 not havewell defined dotsfthe shadow dots (in.

the lightest portions of the negative) must be essentially larger thannormally usual and the lights (the darkest portions of the negative)must be closed a little more than in case of screened 2o negativeshitherto used in the chemigraphy.

In the first continuous-tone negative the lights shall have only adelicateblackening; but within the range of this delicate blackening thelights must have an extremely high contrast. This result is obtained byvery short exposure of a sensitive film, the index of gradation .ofwhich is very high (steep characteristic curve), and by utilizing adeveloper which automatically limits the blackening within the lightestportions. The second continuous-tone negative is ob? tained from asensitive film with a mean or less high index of gradation; whereby thefilm is highly super-exposed and developed by a develop er which alsolimits the blackening automatically.

From the three negatives thus obtained the screened work copy may I. i.be produced in the following manner:

The three negatives an unexposed sensi-- tive film are superimposed sothat in the direction of the printing light the films are lying behindeach other in the sequence: first continu ous-tone negative, screenednegative, second continuous-tone negative, unexposed film. Thereafterthe unexposed film is exposed through the three negatives. The secondcontinuous-tone negative is removed and the exposure repeated.

The twice exposed film is then developed, fixed.

toned down, until the highest lights are free from dots, and finallytreated by means of an intensifier, so that the finest dots aresuillciently covered or blackened for the purpose of printing.

In the described method the quality of the reproduction essentiallydepends upon the corrective efllciencyof the second continuous-tonenegative, which controls the tone or tint values y es comprisesproducing a main or screened negof the screened negative'within theshadows and which therefore is responsiblefor the production of welldefined contours particularly between such portions and points of thereproduction which highly contrast with each other. In producing thissecond continuous-tone negative it'is therefore to be considered thatbesides limiting the blackening the creation of light courts or halos iscarefully avoided.

I have found that the production of the second negative is essentiallysimplified thereby that for its developing a developer is used which iscomposed of an aqueous solution of pyrocatechin and an aqueous solutionof alkali carbonate (potash, sodium carbonate or mixtures thereof). Assuch adeveloper not only avoids the creation of halos but also limitsthe blackening of the negative, it can also be'utilized with greatadvantage. for developing the first continuous-tone negative whichcontrols the tone or tint values of the screened negative within thelights.

I have i. i. obtained very satisfying results by using a developercomposed of practically equal parts ofa solution of about 5 g.pyrocatechin in 1000 ccm. water and of a solution of about 40 g. 25potash in 1000 ccm. water. The quantity of pyrocatechin in the firstsolution and the quantity of potash in the second solution may be variedwithincertain limits. In any case, how ever, it is recommendable'tomaintain the rela tion 5:40 between pyrocatechin and potash.

It is to be considered that the developer is not stable; it decomposesafter about 10 minutes.

. Therefore it is n that the developer is What I claim is:

1. The process for producing a screened work copy of an original to bereproduced; which proc- 40 ative of said original having. the shadowdots thereon vlarger than normal and the fights closed more than normal,subjecting a sensitive film to a very short exposure to produce a firstcontinuous-tone negative of said original, developing and fixing saidfirst continuous-tone negative in a developer composed of an aqueoussolution of pyrosensitive film to high over-exposure to produce a secondcontinuous-tone negative of said original, developing and fixing saidlast mentioned negative, and superimposing the three negatives upon asensitive film and exposing the negatives upon said sensitive film. v

2. The process for producing a screened work I.

- catechin and an alkali carbonate, subjecting a; r

- copy or an original to be reproduced, which process comprisesproducing a main or screened negative of said original having the shadowdots thereon larger than normal and the lights closed more than normal,subjecting a sensitive film ,to a very short exposure to produce a firstcontinuous-tone negative of said original, developing and fixing saidnegative in a developer composed of substan-v tially equal parts of asolution or 5 g. pyrocatechin in 1000 ccm. of water and a solution 01-40g. potash in 1000 ccm. of water, subjecting a second sensitive film tohigh over-exposure to produce a second continuous-tone negative of saidoriginal,

developing and fixing said last mentioned negative, and superimposingthe three negatives upon j a sensitive film and exposing the negativesupon said sensitive film.

3. The process for producing a screened work copy of an original to bereproduced, which proc-' ess comprises preparing a main or screenednegativehaving the shadow dots thereon larger than normal and the lightsclosed more than normal,

" subjecting asensitive film to very short exposure to produce a firstcontinuous-tone negative wherein the lights have a delicate blackening,de-

, veloping and fixing said continuous-tone nega tive, preparing a secondcontinuous-tone'nega tive by over-exposing a sensitive film, developingand fixing the second continuous-tone negative in a developer composedof an aqueous solution of pyrocatechin and an alkali carbonate, superimposing the three negatives thus produced up n normal and the lightsclosed more than normal,

subjecting a sensitive film to very short exposure to produce a firstcontinuous-tone negative wherein the lights have a delicate blackening,developing and fixing said continuous-tone negative, preparing a secondcontinuous-tone negative by over-exposing a sensitive film, developingand fixing the second continuous-tone negative in a developeressentially comprising substantially equal parts of a solution of 5 g.pyrocatechin in 1000 com. 01 water and a solution of 40 g. potash in1000 com. or water, superimposing the three negatives thus produced uponan unexposed film,

with the screened negative intermediate the continuous-tone negatives,exposing the unexposed film through the superimposed negatives, removingthe second continuous-tone negative and again exposing the superimposednegatives, de-

veloping, fixing and toning down the twice exposed film. I

WILHELM SCHUPP.

